Sailboats require more or less sail area for efficient propulsion corresponding to lower or higher wind strengths and to lower or higher apparent wind velocities resulting from varying courses relative to true wind direction. The effectiveness of sails is greatly influenced by control of the flow of air over them. Factors in effecting such control include their position relative to the wind, their shape, particularly the shape of the leading edge, and their size.
The traditional configuration of sail attached to the trailing edge of the mast produces turbulent flow and reduced lift, i.e. effectiveness. Customary reduction of sail area involves partial lowering of the sail and its securing to the boom or winding it up on a rotatable member in a hollow mast (U.S. Pat. No. 3,835,804). Increasing available sail area requires spreading of additional units of sail. Attempts to eliminate undesirable air flow have led to more and more complex, sophisticated, and expensive mast and rig systems and more burdensome demands on crews. For example, U.S. Pat. No. 4,061,101 discloses a doubled sail with improved air foil characteristics on a single boom, the sail being capable of being wound up within a sheath which is part of the mast. A traditional sail which may be rolled on a rotatable mast is shown in U.S. Pat. No. 2,107,303.
It would be desirable to provide a sailboat rig which would at once ensure smooth and efficient airflow over a desired area of sail, quick and easy increase or reduction of that area, and simple control of sail on all points of sailing, and which would satisfy these goals with simple, sturdy construction, eliminating the need for complex systems of stays, shrouds, trunbuckles, vangs, reefing lines, and all other costly and failure prone paraphernalia, and thus simplifying maintenance and crew demand while ensuring efficient performance under sail.
The object of the invention is to provide just such a rig, employing a doubled sail, twin booms and rotatable mast system permitting use of the doubled sail in conventional manner for sailing close to the wind, but readily doubling the effective sail area when sailing on a reach, directly before the wind or to windward in very light air. In either mode of operation the sail provides improved air foil characteristics with reduced turbulence caused by the presence of the mast.